You can add the IP to your firewall. I´m not sure how you can setup this with your shown log-entries. I use postfix with postscreen and add blocked IPs to the firewall using syslog-ng. This could be done also with rsyslog.

As mentioned above you can´t use these log-lines (just connect and disconnect) with fail2ban. Otherwise you will block EVERY connection. You better give postscreen a try.... http://blog.schaal-24.de/?p=661&lang=en